This invention relates to low pressure gas discharge lamps such as fluorescent lamps and the circuitry for driving low pressure gas discharge lamps. Specifically, this invention relates to a fluorescent lamp which is capable of operating as an active circuit component in its own driving circuitry.
This application is related to copending application Ser. No. 744,190 entitled "GAS DISCHARGE LAMP WITH GRID AND CONTROL CIRCUITS THEREFOR" filed Aug. 12, 1991 and assigned to the same assignee as this application.
Fluorescent lamps are in wide use because of their relatively high efficiency, low cost and long life. A fluorescent lamp is a low pressure mercury gas discharge lamp. As with all gas discharge lamps, fluorescent lamps have a negative resistance characteristic and require ballast circuitry to prevent current runaway. For many years the conventional ballast has been a copper/iron choke. However, in recent years, electronic ballasts for gas discharge lamps have become increasingly popular in the lighting industry. Apart from being more efficient than the conventional choke, the electronic ballast is lighter and offers the possibility of adding additional control features to the lamp such as dimming and lamp power stabilization. A disadvantage of electronic ballasts is their high price due in part to their requirement for the use of relatively expensive solid state power switches in the control circuitry. A solid state power switch is relatively expensive and must carry large amounts of current. As such, the heat generated by a solid state power switch is not inconsequential and must be factored into the design of the ballast circuitry.
In current industry practice fluorescent lamps and their driving/ballast circuitry are usually designed by different groups of engineers. New lamp designs are designed by one team of engineers, without concern for driving circuitry, and "thrown over the wall" to the ballast designers. Conversely, new ballast designs may be designed without concern for the lamps they will drive. This can lead to lamps and driving circuitry which are at best, not optimized to work together or at worst, incompatible. The present invention provides a lamp design in which the lamp itself functions as part of its own driver circuitry. The lamp itself operates as its own active high current component eliminating the need for high current devices in the electronic ballast/driving circuitry.